多孔介质内天然气水合物原位分解过程微观传质控制机理

Enormous natural gas hydrate resources have been discovered in China. Their safe and efficient exploitation is considered to be a major concern of national energy demand. The gas recovery process from gas hydrate resources in deposits is a complicated phase transition process in porous media, coupling with micro-scale mass and energy transfer. The microstructure evolution of gas hydrate, micro-scale gas and water transfer, and mechanism of secondary hydrate formation during pore-scale hydrate decomposition are the fundamental scientific issues in terms of gas hydrate resource utilization. Under this research background, this project is expected to build a microstructure visualization system of gas hydrate during in-situ decomposition and an identification and tracking technique of phase interfaces. The time-dependent characteristics of multi-phase interfaces during in-situ hydrate decomposition and the micrometer-resolution decomposition rates of gas hydrate are studied. The obtained metastable enrichments of gas in trapped water pockets during initial hydrate decomposition would give some implications in the mechanism of secondary hydrate formation on the hydrate surfaces. The gradient of gas concentration in the water layers towards gas phase is determined, which indicates the limiting mechanism of the water layers on the diffusion of gas molecules from the hydrate surfaces to the gas phase. These findings would help further understand the micro-mechanism of in-situ gas hydrate decomposition in porous media, and provide theoretical foundation to the efficient exploitation of gas hydrate resources in China.

我国天然气水合物资源储量巨大，实现其安全高效开发是国家重大能源需求。沉积层中天然气水合物资源的开发过程是多孔介质内伴随微尺度气、水传质与能量传递的复杂相变过程，孔隙尺度天然气水合物原位分解过程微观形态结构演变规律，气、水微尺度传质特性，以及二次相变诱发机制是天然气水合物资源利用亟需解决的关键问题。本项目以此为背景，建立天然气水合物原位分解微观可视化系统与相界面识别与跟踪技术，获得多孔介质内天然气水合物原位分解过程多相界面时变特性，揭示微米分辨率水合物原位分解速率时间依赖规律；探究分解初期束缚水中气体亚稳态过饱和富集形态，阐明其对原位分解过程水合物表面二次相变诱发机制；获得原位分解过程水合物表面水层中气体浓度梯度分布，揭示水合物表面自由水层对气体分子扩散传质抑制机制，最终探明多孔介质内水合物原位分解微观传质控制机理，为我国天然气水合物资源高效开采提供理论依据。

海洋天然气水合物资源开发涉及了多孔介质内伴随相变的气、水传质与能量传递复杂过程，认识分解界面微观传质规律，是解答水合物开采高效性问题的关键。本项目以此为背景，基于X射线成像技术与激光微纳颗粒跟踪技术，获得了多孔介质内天然气水合物原位生成、分解过程多相界面时变特性，刻画了水合物壳内气体分子微观传质过程；揭示了水合物原位分解速率时间依赖规律，发现了初期束缚水中气体亚稳态过饱和富集形态，提出了水合物表面自由水层对气体分子扩散传质抑制机制；建立了水合物-水界面分解分子动力学模型，精细描述了界面分解气体分子溶解扩散传质过程，最终探明气体传质主导的多孔介质内水合物原位分解微观控制机理。